Means for coupling concentric cavity resonators



Oct. 10, 1950 A. M. GUREWITSCH MEANS FQR COUPLING CONCEN'I'RIC CAVITY RESONATORS Filed Juno 3, 1949 lung Zh-E

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Inventor- I Anatole m. G urewicsch,

by fmf/ His At zgiy Patented Oct. 10, 1950 MEANS FOR COUPLING CONCENTRIC CAVITY RESONATORS Anatole M. :Gurewitsch, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 3, 1949, Serial No. 97,071

2 Claims. 1 My invention relates to improved means for coupling concentric cavity resonators.

At ultra-high frequencies where wave lengths between a few meters and a few centimeters are utilized in amplifier and oscillator circuits, concentric space-resonant cavities defined between three telescoped and radially separated conductors are often used in combination with an electron discharge device having its grid coupled to the intermediate conductor and its anode and cathode coupled respectively to the remaining conductors.

Whether such a resonator apparatus is used as'an oscillator or as an amplifier, the means for coupling the two concentric space-resonant cavities to provide a definite energy disposition between them is of great importance. While some coupling usually exists because of internal capacitance of the electron discharge device, it is often desired to augment this internal coupling by providing additional feed-back energy, as in oscillator circuits, or to neutralize the internal coupling as in amplifier circuits. Such coupling means, which may be externally adjusted to vary both the phase and magnitude of the coupling energy through a wide range, are not only desirable but are necessary in many applications. While adjustable coupling impedance arrangements have been satisfactorily used in laboratory apparatus, they are usually too complicated or cumbersome in practical applications.

It is an object of the present invention to provide a means for coupling concentric spaceresonant cavities which is characterized by compactness and by ease of operation.

It is a further object of my invention to provide an improved adjustable coupling impedance for concentric cavities.

According to my invention, I employ as a coupling impedance a tunable concentric transmission line section which is coupled to a concentric cavity resonator. The outer coupling conductor is connected to the outer conductor of the resonator, and the inner coupling conductor extends through the outer and intermediate cavity conductors for capacitive coupling with the inner cavity conductor. In order to permit adjustment of the phase of the feedback energy, the outer end of the transmission line section is terminated by a plunger which is slidable to vary its electrical length. The magnitude of the feedback energy is adjusted mainly by axially moving the inner coupling conductor to vary the capacitance coupling with the inner cavity conductor. By suitably varying the phase and magnitude of the feedback energy in the coupling impedance, the

desired operating characteristics of the resonator system may be obtained. To extend the range of variation of the feedback energy, I additionally employ in another embodiment of my invention an intermediate concentric conductor attenuator connected to the intermediate resonator conductor and extending radially into the outer coupling conductor. The additional conductor is dimensioned so that it acts as a wave guide below the cut-off frequency of the resonator, and hence attenuates the coupling energy within it according to the distance from the inner resonator conductor. With the inner conductor of the coupling impedance adjustably positioned within the attenuator conductor, the magnitude of the feedback energy is more easily controlled, and in addition, since the energy transferred from one cavity to the other must travel along the length of the attenuator section and back, the physical length of the outer coupling may be shortened for greater compactness.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the ap-- pended claims. In the drawings, Fig. 1 shows an embodiment of my invention in a concentric cavity resonator apparatus and Fig. 2 represents a modification of my invention.

Referring now to the drawing, cavity resonator apparatus comprising three concentric and mutually telescoped conductors I, 2, and 3, suitably consisting of brass and copper, is illustrated in Fig. 1. An electric discharge device 4 having planar co-axially aligned elements is coupled to the concentric conductors at one end of the resonator apparatus. The anode terminal means 5 of the discharge device is inserted in the end of outer conductor I of the resonator. A control electrode or grid 6, which comprises a planar disk, is similarly fitted within the endof the intermediate resonator conductor 2, and the cylindrical cathode 1 is connected to the inner resonator conductor 3. This type of discharge device and its mode of connection to a concentric cavity is more fully described in Letters Patent 2,446,017, issued to E. D. McArthur, et al., and assigned to the assignee of the present invention. If desired, a discharge device so arranged that the anode is coupled to the inner conductor and the cathode is coupled to the outer conductor of the resonator apparatus may be substituted for the discharge device 4 shown in the Fig. 1 without departing from the spirit of my invention.

By virtue of their mutual spacing, the concentric conductors provide in effect a pair of concentric transmission line sections, each of which by proper termination can be made to function as a space resonant cavity. Accordingly, the outer transmission line section is tuned by a choke 8 which is slidably mounted on the intermediate conductor 2 and has a cylindrical surface concentric with the outer conductor I and insulatingly spaced therefrom. The design and function of ultra-high frequency chokes is well known and will not be described here. It is to be understood, of course, that other suitable means for tuning the transmission line sections formed by the conductors I, 2, and 3 may also be employed. For example, if the proper bypassing capacitance is otherwise provided, a short-circuiting plunger may also be used between conductors l and 2. To tune the outer or anodegrid cavity defined by the conductors I and 2, the choke may be moved along conductor 2 to a desired position by suitable actuating rods 9 connected to it and projecting from the end of the conductor I. A similar choke i is provided between conductors 2 and 3 to tune the inner or grid cathcde cavity defined between them. Actuating rods Ii connected to the inner choke 50 may be used to vary its position along the length of the conductors. Energy is extracted from the anode grid cavity by any suitable output electrode means, one form of which may be a capacity coupling defined by a metal plate 52 in spaced relation with the outer surface of the intermediate resonator system conductor 2 at a point of high electric field intensity. The plate I2 is connected to a concentric transmission line comprising an inner conductor l3 and an outer conductor :4 conductively supported from the outer surface of the outer resonator system conductor l.

A concentric line coupling impedance l5 which may be suitably made of brass or copper tubing is employed adjustably to couple the inner and outer cavities of the concentric resonator in order to provide feedback energy of the desired phase and amount. The outer coupling conductor it of the concentric line impedance is conductively supported at one end thereof to the outer conductor 4 of the resonator system to couple it with the outer space resonant cavity. The inner coupling conductor IT extends beyond the supported end of the outer coupling conductor into the inner resonant cavity. By reason of the spaced relationship between the end is of the coupling conductor I? and the inner resonator system conductor 3, the inner spaceresonant cavity is capacitively coupled with the concentric line coupling impedance.

The inner end of the conductor l8 preferably carries a conductive plate or has an otherwise enlarged area to permit as substantial a degree of coupling as desired at the minimum spacing. The desired phase relationship of the feedback energy is achieved by tuning the concentric line section comprising coupling conductors l6 and H with a slidable terminating means such as a shortcircuiting plunger i9 which is slidably adjusted along the length of the concentric line impedance by actuating rods 20. The inner coupling conductor H is slidably mounted through a central aperture in the plunger I 9 and the end portion 2| extending through the plunger serves as an actuating means for axially moving the inner conductor independently of plunger means [9.

When the discharge device 4 is operated to energize the concentric space resonant cavities, the couplin impedance i5 is adjusted to provide the desired transfer of energy between the gridanode cavity and the grid-cathode cavity by moving the inner coupling conductor 11 to principally control the amount of coupling energy and by moving the plunger I9 to tune the concentric line section to provide the desired phase relation between the space resonant cavities. It is to be understood, of course, that while some coupling between the anode and cathode of the discharge device may exist because of internal capacitances between those elements, my adjustable coupling means is employed to either supplement or counteract any such inherent coupling.

In the modification of my invention illustrated in Fig. 2, conductors 22, 23, and 24 corresponding to conductors I, 2, and 3 in Fig. 1 define between them a pair of concentric space resonant cavities which are suitably terminated by choke means 25 and 26. In this modification, the coupling impedance also comprises a tuned concentric line section 21 having an outer conductor 23 conductively supported at one end by the outer conductor 22 of the concentric cavity resonator and having a slidable inner conductor 29 capacitively coupled to inner conductor 24 of the resonator. In addition, a third concentric conductor 30 which functions as an attenuator is connected to the intermediate conductor 23 of the resonator. The attenuator 30 surrounds the inner conductor 29' of the coupling impedance and partiall extends within the outer conductor 23 of the coupling impedance. The additional conductor 36 is suitably made of brass or copper tubing and has a sufficiently small cross section dimension to serve as a wave guide below cutoff of the frequency of the inner cavity energy. Between the end of the coupling impedance electrode 29 and inner conductor 24 of the concentric resonator the attenuator provides a definite means for decreasing the field intensity as a function of the distance from the center conductor of the resonator, and hence facilitates the use of the coupling electrode 29 for controlling the amount of feedback energy to be transferred. As shown in Figure 2, a short conductor 3! is preferably connected to the inner cavity conductor 24, which conductor extends toward the coupling electrode 29 to help guide some of the inner cavity energy into the attenuator 30.

The modified coupling impedance illustrated in Fig. 2 is operated in the same manner as the apparatus described in Fig. 1. However, in addition to the increased facility of control of the amount of coupling energy by the use of the attenuator 30, the conducting wall of that attenuator section also provides a longer space path for the energy between the inner and outer cavities of the resonator so that a shorter outer conductor 28 may be employed in the impedance coupler to obtain the same range of phase adjustment.

While the present invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is: p

1. In an ultra-high frequency electrical apparatus comprising three telescoped conductors providing between them a pair of concentric cavity resonators, a concentric line coupling impedance for coupling said resonators which comprises an inner coupling conductor having one end capacitively coupled to the inner conductor of said three conductors, the intermediate and outer conductors of said three conductors being suitably apertured to receive said coupling conductor, an outer coupling conductor having one end coupled to the outer conductor of said three conductors, a tubularattenuator conductor concentrically disposed between said inner and outer coupling conductor having one end conductively supported by the intermediate conductor of said three conductors, said tubular attenuator conductor being dimensioned below cut-off of the frequency of the energy in said resonator apparatus, and means interposed between said inner and outer coupling conductors at a position beyond the other end of said attenuator conductor to determine the effective length of said concentric line coupling impedance.

2. In an ultra-high frequency electrical apparatus comprising three telescoped conductors providing between them a pair of concentric cavity resonators, a concentric line coupling im- 3 6 of said three conductors, the intermediate and outer conductors of said three conductors being suitably apertured to receive said coupling con ductor, said coupling conductor being axially movable to vary the magnitude of said coupling, an outer coupling conductor having one end coupled to the outer conductor of said three conductors, a tubular attenuator conductor concentrically disposed between said inner and outer coupling conductor and havin one end conductively supported by the intermediate conductor of said three conductors, said tubular attenuator conductor being dimensioned below cut-off of the frequency of the energy in said resonator apparatus, and means interposed between said inner and outer coupling conductors at a position beyond the other end of said attenuator conductor to determine the effective length of said concentric line coupling impedance, said means being movable to vary the phase relation between ultra-high frequency energy in said resonators.

ANATOLE M. GUREWITSCI-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 7 Name Date 2,427,558 Jensen Sept. 16, 1947 2,446,405 Bels Aug. 3, 1948 2,461,125 Nergaard Feb. 8, 1949 

